fix(agents): scope claude-cli fallback seed and pair summary with boundary

Addresses review on #72069:

- Codex P1 ("Gate Claude prelude seeding by source provider"): the
  guard checked the *current* fallback candidate but not the failed
  attempt. A session that still carried a stale
  cliSessionBindings["claude-cli"] from an unrelated past run would
  inject Claude transcript context into a fallback chain that started
  on a different provider (e.g. openai -> openai-codex), leaking
  irrelevant prior conversation. Plumb `originalProvider` (the
  user-requested provider for the chain) through to runAgentAttempt
  and require `isClaudeCliProvider(originalProvider)` before reading
  Claude history.

- Codex P2 ("Prefer latest compact boundary when summary is missing"):
  the resolver always preferred the most recent explicit summary, so
  a later compaction without its own summary entry (rare crash case)
  paired stale summary text with post-latest-boundary turns. Restructure
  readClaudeCliFallbackSeed to queue summaries into pendingSummary and
  flush each boundary's pair atomically. A boundary with no preceding
  summary now correctly falls back to the boundary's own content
  rather than serving an older summary alongside fresh turns.

- Greptile P2 (newest-first break vs sparse coverage): the
  formatFallbackTurns walk intentionally stops on the first oversized
  turn so the prelude stays a contiguous "what was happening just
  before the failure" window. Document the design choice inline so a
  future maintainer doesn't reflexively change it to skip-and-continue.

Tests:
- New gateway cases for the boundary-without-summary edge case and
  for trailing summaries written without a paired boundary.
- existing 33 attempt-execution + 14 cli-session-history tests still
  pass; broader src/agents/command suite stays green (63/63).

src/agents/agent-command.ts

@@ -954,6 +954,7 @@ async function agentCommandInternal(
             return attemptExecutionRuntime.runAgentAttempt({
               providerOverride,
               modelOverride,
+              originalProvider: provider,
               cfg,
               sessionEntry,
               sessionId,